1. Field of the Invention
The present invention relates to a packet congestion control method in a packet communication system and to packet switching equipment using the same
2. Description of the Prior Art
In high-speed packet communication, in order to improve the transfer throughput in the network, there has been a tendency to adopt a switch in which the operation of the packet switching equipment is simplified so as to carry out the primary portion of the operation by means of hardware. For example, there has been proposed an asynchronous transfer mode (ATM) as means of effecting a high-speed packet communication in which a fixed-length cell is employed.
In these systems, packets are communicated by use of an information channel for transferring through the network in a transparent fashion information packets to be communicated between packet communication equipment and a control channel for transferring control packets controlling the information channel for call set-up/release, etc.
For a packet transferred through an information channel, the packet switching equipment or the packet switch switches a logical channel number representing an identification of the packet and performs an indispensable minimum processing, such as error detection on the packet. Namely, the packet switch does not conduct processing for an acknowledgment. (A sequence of processing achieved by the packet switch will be referred to as a frame relay here below).
Furthermore, for a control packet to be transferred through a control channel, each packet switching equipment performs a sequence of processing such as a data link setup and a data link release, and processing for a routing operation. In consequence, the transfer rate of a packet on the control channel is less than that developed on the information channel.
Between packet communication equipment (terminals), for example as shown in FIG. 31, packet communication equipment 50a transmits a packet onto a line 91a such that the packet is subjected to a store-and-forward type switching through packet switches 60a to 60c so as to be transferred to packet communication equipment 50b. However, as shown in FIG. 31, since the switches are connected to many lines 91a to 91j, when a large number of packets from plural lines are concentrated on the packet switch 60c, the buffer memory for storing the packets becomes to be insufficient in the packet switch 60c, which can lead to a loss of packets (this event is referred to as a congestion herebelow).
In order to prevent deterioration of quality of packet transfer in a network due to lengthy congestion, when a congestion occurs on an information channel, the occurrence of the congestion is required to be reported to the packet communication equipment to restrict the packet flow rate of packets transmitted onto the information channels.
However, a method to indicate the congestion by use of the control channels takes a considerable period of time for the delivery of the notification to the packet communication equipment and hence is not suitable for the restriction of the flow rate of packets on the information channels.
According to JP-A-63-24742 (Laid-open on Feb. 2, 1988), congestion information is added to an acknowledgment packet on an information channel between packet communication equipment and to a monitoring packet therebetween to identify the congestion to the packet communication equipment, thereby solving this problem.
In the prior art technology above, proper consideration has not been given to the processing load imposed on the packet communication equipment. In consequence, for a communication in which an acknowledgment is not required between packet communication equipment, it is necessary to use a monitoring packet for continuously monitoring congestion, which leads to a problem of increased processing load associated with the transmission of the monitoring packet.
Furthermore, until the packet communication equipment which has received a packet transmits an acknowledgment packet, the congestion cannot be identified to the packet communication equipment operating as the transmission source; in consequence, there has been a problem that a long period of time typically elapses from an occurrence of congestion to when the packet transmission is restricted by the packet communication equipment.
Furthermore, even in a case other than the case of congestion, a packet invalid on an information channel is required to be transferred to process the monitoring packet in the network, which leads to a problem that the effective transfer throughput of the information channel is lowered.